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Consulting With Clouds: A Clear Role in Climate Change

Virginia Key, Fla. —
The role of clouds in climate change
has been a major question for decades. As the earth warms under
increasing greenhouse gases, it is not known whether clouds
will dissipate, letting in more of the sun’s heat energy
and making the earth warm even faster, or whether cloud cover
will increase, blocking the Sun’s rays and actually
slowing down global warming.

In a study published in the July 24 issue of Science,
researchers Amy Clement and Robert Burgman from the University
of Miami’s Rosenstiel School of Marine and Atmospheric
Science and Joel Norris from Scripps Institution of
Oceanography at UC San Diego begin to unravel this
mystery. Using observational data collected over the last
50 years and complex climate models, the team has established
that low-level stratiform clouds appear to dissipate as the
ocean warms, indicating that changes in these clouds may
enhance the warming of the planet.

Because of inconsistencies in historical observations, trends
in cloudiness have been difficult to identify. The team
broke through this cloud conundrum by removing errors from
cloud records and using multiple data sources for the northeast
Pacific Ocean, one of the most well-studied areas of low-level
stratiform clouds in the world. The result of their analysis
was a surprising degree of agreement between two multi-decade
datasets that were not only independent of each other, but that
employed fundamentally different measurement methods. One set
consisted of collected visual observations from ships over the
last 50 years, and the other was based on data collected from
weather satellites.

“The agreement we found between the surface-based
observations and the satellite data was almost shocking,”
said Clement, a professor of meteorology and physical
oceanography at the University of Miami, and winner of the
American Geophysical Union's 2007 Macelwane Award for her
groundbreaking work on climate change. “These are subtle
changes that take place over decades. It is extremely
encouraging that a satellite passing miles above the earth
would document the same thing as sailors looking up at a cloudy
sky from the deck of a ship.”

What was not so encouraging, however, was the fact that most of
the state-of-the-art climate models from modeling centers
around the world do not reproduce this cloud behavior. Only
one, the Hadley Centre model from the U.K. Met Office, was able
to reproduce the observations. “We have a long way to go
in getting the models right, but the Hadley Centre model
results can help point us in the right direction,” said
co-author Burgman, a research scientist at the University of
Miami.

Together, the observations and the Hadley Centre model results
provide evidence that low-level stratiform clouds, which
currently shield the earth from the sun’s radiation, may
dissipate in warming climates, allowing the oceans to further
heat up, which would then cause more cloud dissipation.

“This is somewhat of a vicious cycle potentially
exacerbating global warming,” said Clement. “But
these findings provide a new way of looking at clouds changes.
This can help to improve the simulation of clouds in climate
models, which will lead to more accurate projections of future
climate changes. ”

One key finding in the study is that it is not the warming of
the ocean alone that reduces cloudiness -- a weakening of the
trade winds also appears to play a critical role. All models
predict a warming ocean, but if they don’t have the
correct relationship between clouds and atmospheric
circulation, they won’t produce a realistic cloud
response.

“I am optimistic that there will be major progress in
understanding global cloud changes during the next several
years,” said Norris. “The representation of
clouds in models is improving, and observational records are
being reprocessed to remove spurious variability associated
with satellite changes and other problems.”

Both Clement and Norris, who is a professor of atmospheric and
climate science at Scripps, have received National Science
Foundation Faculty Early Career Development awards for their
work on climate change. The National Oceanic and Atmospheric
Administration Climate Program Office also provided support for
this research.

AboutScripps Institution of Oceanography
Located at the University of California, San Diego, the Scripps
Institution of Oceanography is one of the oldest, largest and
most important centers for global science research and
education in the world. The National Research Council has
ranked Scripps first in faculty quality among oceanography
programs nationwide. Now in its second century of discovery,
the scientific scope of the institution has grown to include
biological, physical, chemical, geological, geophysical and
atmospheric studies of the earth as a system. Hundreds of
research programs covering a wide range of scientific areas are
under way today in 65 countries. The institution has a staff of
about 1,300, and annual expenditures of approximately $155
million from federal, state and private sources. Scripps
operates one of the largest U.S. academic fleets with four
oceanographic research ships and one research platform for
worldwide exploration.

About the University of Miami’s Rosenstiel
SchoolThe University of Miami is the largest private research
institution in the southeastern United States. The
University’s mission is to provide quality education,
attract and retain outstanding students, support the faculty
and their research, and build an endowment for University
initiatives.Founded in the 1940’s, the Rosenstiel
School of Marine & Atmospheric Science has grown into one
of the world’s premier marine and atmospheric research
institutions. Offering dynamic interdisciplinary academics, the
Rosenstiel School is dedicated to helping communities to better
understand the planet, participating in the establishment of
environmental policies, and aiding in the improvement of
society and quality of life. For more information, please visit
www.rsmas.miami.edu